1. Field of the Invention
The present invention relates to a dryer fabric for a papermaking machine, and particularly to a dryer fabric constructed so as to eliminate slack dryer belt edge portions thereby eliminating their effect on the moisture profile of the paper web passing through the dryer section of the papermaking machine, improve tail feeding and fabric guiding.
2. Description of Related Art
U.S. Pat. No. 3,867,766 disloses a typical papermaking machine dryer section. The dryer section of the papermaking machine of this type includes an upper and a lower array of heated, cylindrical rolls arranged and spaced in a staggered, parallel array. A paper web exits from a pressing section of the papermaking machine and enters the dryer section. The paper web is generally passed to and fro between the arrays of dryer rolls in a generally serpentine manner to ensure that both sides of the paper web contact the dryer rolls as may be seen in FIG. 1 of the above U.S. patent. As the paper web passes over a dryer roll, it is held in intimate heat transfer relation therewith by an endless dryer belt as should be apparent from FIG. 1.
U.S. Pat. No. 4,423,543 discloses one known type of dryer belt. This patent discloses a spiral fabric including spiral coils which are laid out in a cross-machine direction. Adjacent spirals are intermeshed with one another to define a hinge yarn receiving opening. The opening receives a hinge yarn, typically a synthetic monofilament, which is inserted into the hinge yarn receiving opening defined by the intermeshed spirals.
While such a known spiral fabric has many positive attributes as a dryer fabric, such as good cross-machine stability resulting in excellent resistance to bowing, availability in a wide range permeabilities, and a high degree of surface smoothness for good contact with a paper web, it has a notable disadvantage. The known spiral fabric is prone to slack edges at which the edges of the spiral fabric may fall away from the dryer cylinder against which it presses.
When a paper sheet is sandwiched between the hot dryer cylinder and the dryer fabric, the dryer fabric presses the paper sheet against the cylinder and holds the sheet in contact with the cylinder, thereby improving heat transfer to the paper sheet. If the edges of the dryer fabric do not press the paper sheet fully against the cylinder, different drying rates in the middle and on the edges of the paper sheet, resulting in non-uniform moisture profile across the sheet, may therefore be produced. In extreme cases this may cause reduced finished paper sheet width because the edge of the paper sheet may need to be trimmed excessively.
Also, when a paper machine starts, a tail, i.e., a narrow edge sheet of paper approximately six inches wide, is first fed through the machine. If the edges of the dryer fabric are slack, feeding of the tail can be difficult and start-up of the machine slowed.
Also, dryer fabrics with slack edges can be difficult to guide because the edge can dip under the guide paddle thereby rendering the guiding mechanism inoperative. In such extreme cases the fabric can then run off the machine and be wrecked beyond repair.
The instant invention is designed to eliminate slack edges in non-woven dryer fabrics to be used in dryer sections of papermaking machines.